Add node label to inventory

This is needed for (at least) the log processor jobs which communicate
information about what labels are used.

Change-Id: I20dc54fcd56c3dfebabe4b7900ac06b729582a83
diff --git a/zuul/executor/server.py b/zuul/executor/server.py
index daa029f..03fcb4a 100644
--- a/zuul/executor/server.py
+++ b/zuul/executor/server.py
@@ -1162,6 +1162,7 @@
                 ansible_user=self.executor_server.default_username,
                 ansible_port=port,
                 nodepool=dict(
+                    label=node.get('label'),
                     az=node.get('az'),
                     cloud=node.get('cloud'),
                     provider=node.get('provider'),